Differential current sensing bussing method

ABSTRACT

The line power and neutral conductors for a circuit interrupter such as a miniature circuit breaker, using ground fault sensing via a current transformer, are arranged as a rigid conductor formed from a flat plate and surrounding and holding an insulated flexible conductor when passing through the Ground Fault Interrupter current transformer. The rigid conductor can provide a shaped current path to maximize the effectiveness of the current transformer.

PRIORITY INFORMATION

The present application is a division of and claims priority to U.S.patent application Ser. No. 15/672,762, filed on Aug. 9, 2017, which isherein incorporated by reference as if fully set forth in thisdescription.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to circuit interrupters that utilizeground fault sensing as part of the fault detection methods, includingcircuit breakers or receptacles, and particularly to ground faultsensing miniature circuit breakers and outlet receptacles found mostcommonly in residential use.

2. Discussion of the Art

FIG. 1 illustrates the basics of a known circuit breaker 10 of theGround Fault Interrupter type with a schematic representation therein ofthe line power current path 11. The line current path starts at the linepower terminal 13 of the breaker 10 and continues through the separablecontacts 15 and a toroidal current transformer current sensor 17 to theload terminal 18 which is wired out to the branch load 22, hererepresented as a motor. A mechanical “side” or portion 16 of the circuitbreaker 10 contains thermal and magnetic trip units 19, typically abimetal and a magnetic yoke assembly, respectively, which are componentsfor tripping, i.e. separating, the contacts 15, in the event ofovercurrent conditions.

An electronic “side” or portion 20 of the arc fault sensing circuitbreaker 10 contains the current sensor in the form of currenttransformer 17, and associated electronics 21 for evaluation of GroundFault events. The electronics 21 control an actuator 23, typically asolenoid, whose function is also to trip the separable contacts 15 andremove power from the load 22.

The return neutral current path 24 from the load 22 travels from theload 22 to the neutral terminal 28 through the current transformercurrent sensor 17 and out to the neutral return wire 26. It will beappreciated that a plug on neutral type breaker will have a terminalclip rather than, or in addition to, the illustrated pigtail wire.

The current flow direction of the power conductors and the neutralconductors are in the opposite directions when they are routed throughthe Ground Fault current transformer 17 sensor housing. Each currentcarrying conductor will produce a magnetic flux which is in compliancewith the “Right Hand Rule” used to determine flux direction. When thetwo conductors are carrying the same level of current in oppositedirections, the flux of one conductor will cancel the flux from theother conductor. This then has a net flux value of zero. If there is anequal current exiting and then returning back through the Ground Faultcircuit breaker, the Ground Fault sensor will output no signal. If thereis an imbalance of current in the circuit wires, then the Ground FaultInterrupter sensor will output a current proportional to the currentimbalance and if this imbalance exceeds a predetermined threshold, theGround Fault circuit breaker will detect the presence of a ground faultand interrupt the electrical circuit.

A recognized problem with Ground Fault Interrupter sensors is that ifthe conductors are not located properly in the sensor, uneven magneticfields throughout the current sensor assembly can cause an outputcurrent from the current sensor, even when the total current through theconductor paths are balanced. The result is an inaccuracy in the currentsensor output known as load shift error. Typically this error iscompensated for by twisting the main conductors (line and neutral) asthey pass through the Ground Fault current transformer. It has beenproposed, e.g. by U.S. Pat. No. 3,725,741 to Misencik, to replace theusual twisted pair of main conductors (line and neutral) with a rigidtubular outer conductor surrounding an insulated flexible conductorpassing through the aperture of the Ground Fault Interrupter currenttransformer.

SUMMARY OF THE INVENTION

The line power and neutral conductors for a Ground Fault sensinginterrupter are arranged as an improved rigid conductor surrounding andholding an insulated flexible conductor when passing through the currentsensing transformer. The rigid conductor may be shaped to providecontrolled current flow distribution for adjusting any ground fault loadshift through the current transformer and more evenly distributing themagnetic field through the current transformer. Conversely, in someaspects of the invention a deliberate ground fault load shift may beprovided by the apparatus if desired.

A Ground Fault current sensing package according to the presentinvention utilizes a so-called “faux coax bus bar” i.e. a rigidconductor encompassing and holding a flexible insulated conductor,passing through the current transformer core in place of twisted wiresto help control ground fault load shift performance inside the GroundFault current sensor. Aspects of the present invention can be used tocontrol current distribution across the faux coax for a better outputfrom the current sensor. The faux coax arrangement also provides foreasier construction while also eliminating the need for a twisted wireassembly and maintaining a more consistent routing path for the Line andNeutral wires to obtain a more consistent load shift performance.

In one aspect, the present invention provides for a Ground Fault sensingminiature circuit breaker with line power and neutral power currentpaths within an apertured current transformer for the detecting ofground fault current anomalies, comprising: a rigid conductorsurrounding and holding a flexible conductor; the rigid conductor andthe flexible conductor passing through the aperture of the Ground Faultcurrent transformer inside of the miniature circuit breaker with therigid conductor being shaped to control current density, and resultantflux, within the core.

In some aspects of the present invention the rigid conductor isconnected to and forms a part of the current path of the Neutralconnection. Alternatively, the rigid conductor could form a part of theLine power connection and the neutral line could be connected throughthe flexible conductor encompassed and held by the rigid conductor. Therigid conductor may be formed from a flat blank having first and secondterminal strips and a wider central portion which has been rolled into asubstantially tubular form for fitting through the current transformer.The rigid conductor can also have current density directing featuresintegrated therein to create increased resistance to the flow of currentsuch as where the electrical resistance feature in the rigid conductoris created by a narrowed wall thickness or through hole in the sectionof the substantially tubular form. Also for example the tubular formmight, e.g., be formed by a roll of 180 degrees or 270 degrees betweeninput and output terminals to control current flow and flux patterns.

Other aspects of the present invention offer an improvement to a Groundfault interrupter apparatus of the differential transformer type such asa miniature circuit breaker of the ground fault sensing type comprising:a current transformer with an apertured magnetic core; a printed circuitboard with electronics for detection of ground fault events; first andsecond primary conductors extending through the core; the first primaryconductor being a substantially rigid conductor with a tubular portionlocated inside the core and further having nontubular second and thirdportions outside the core extending at angles to the tubular portion,one of the second or third portions secured to the printed circuitboard; the second primary conductor being a flexible wire held insidethe tubular portion of the first primary conductor in a substantiallycoaxial arrangement; the current sensor further having a secondarywinding comprising a plurality of turns on the core; a trip circuitresponsive to sensed signals on the secondary winding. In some aspectsof the invention the rolled central portion does not necessarily form afully closed tube. Other aspects of the present invention present animprovement comprising the rigid conductor being formed by starting froma flat conductive piece and having a rolled central portion of the flatpiece thereby creating the tubular conductor and flat terminal strips.Again, features may be added to the structure of the rigid conductor toprovide shaped current flow, wherein the features can includethrough-holes in the wall of the rolled central portion or includenarrowed wall thickness in the wall of the rolled central portion. Itwill be appreciated upon understanding the present invention that therigid conductor can provide other current routing advantages within thecircuit interupter such as the elimination of jumper wires.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the disclosed embodiments willbecome apparent upon reading the following detailed description and uponreference to the drawings, wherein:

FIG. 1 is a schematic illustration of the working parts of an exemplaryground fault or dual function circuit breaker as known in the art.

FIG. 2 is a perspective view of the interior of the mechanical side of adual function circuit breaker of the present invention;

FIG. 3 is a perspective view of the electronics side of the circuitbreaker of FIG. 2 of the present invention;

FIG. 4 is a perspective view of a Dual Function circuit breaker PCB withthe integrated arc fault and ground fault current sensing package of thepresent invention utilizing one ground fault current transformer.

FIGS. 5-25 detail various alternative embodiments of the rigidconductor.

DETAILED DESCRIPTION

As an initial matter, it will be appreciated that the development of anactual commercial application incorporating aspects of the disclosedembodiments will require many implementation specific decisions toachieve the developer's ultimate goal for the commercial embodiment.Such implementation specific decisions may include, and likely are notlimited to, compliance with system related, business related, governmentrelated and other constraints, which may vary by specificimplementation, location and from time to time. While a developer'sefforts might be complex and time consuming in an absolute sense, suchefforts would nevertheless be a routine undertaking for those of skillin this art having the benefit of this disclosure.

It should also be understood that the embodiments disclosed and taughtherein are susceptible to numerous and various modifications andalternative forms. Thus, the use of a singular term, such as, but notlimited to, “a” and the like, is not intended as limiting of the numberof items. Similarly, any relational terms, such as, but not limited to,“top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,”“side,” and the like, used in the written description are for clarity inspecific reference to the drawings and are not intended to limit thescope of the invention.

Words of degree, such as “about,” “substantially,” and the like are usedherein in the sense of “at, or nearly at, when given the manufacturing,design, and material tolerances inherent in the stated circumstances”and are used to prevent the unscrupulous infringer from unfairly takingadvantage of the invention disclosure where exact or absolute figuresand operational or structural relationships are stated as an aid tounderstanding the invention.

The person of ordinary skill in the art will appreciate that the wellknown components of an electronic miniature circuit breaker unnecessaryto the exposition of the present invention are not described in detailhere, but will be understood to be present in a functioning circuitinterrupter as briefly explained above. While shown here in the contextof a miniature circuit breaker it will be appreciated by those in theart that the invention may be applicable to a variety of Ground Faultsensing apparatus, such as other forms of circuit interrupter devices,receptacles, or monitoring systems.

FIG. 2 illustrates the “mechanical side,” i.e. portion, of a partiallyconstructed arc fault sensing circuit breaker 30 according to certainaspects of the present invention. The terms “side” and “portion” areused herein to convey the sense of a functional grouping which may ormay not exist as discrete physical layouts within the design of thebreaker. Further, some common reference numbering between FIG. 1 and theremaining figures may be used herein where the component functionalitiesare substantially in common between the two. The line (power) currentpath starts at the line power terminal 13 of the breaker 30 andcontinues through the separable contacts 15 into the movable contact arm70 and travels by wire 72 through the mechanical trip portions of theyoke 74, latch plate 78, and bimetal 76 which cause the mechanical tripby separating the latch plate 78 from the trip lever 80. The currentpath then passes through the Ground Fault Interrupter currenttransformer 34, as further explained below, before exiting to the loadterminal 18 which is wired out to the branch load 22 (FIG. 1).

FIG. 3 illustrates one possible electronic “side,” i.e. portion, 31 ofthe arc fault sensing circuit breaker 30 containing the currenttransformer current sensor 34, and associated electronics 52 mounted toa PCB 50 for evaluation of Ground Fault and Arc Fault events. Theelectronics 52 control a solenoid actuator 53 whose function is also tomove the latch plate 78 from the trip lever 80 to trip the separablecontacts 15 and remove power from the load (not shown). The return(Neutral) current path from the load travels from the Neutral returnterminal 28, which is a second end of the rigid conductor 36, throughthe current sensor current transformer 34, as further explained below,and out to the neutral return wire (pigtail) 26 or the plug on neutralclip 82, both of which are shown here for the sake of explanation.

Referencing particularly FIG. 4, as is understood in the art, thecurrent transformer 34 includes a wound toroidal core within its case.Through the aperture 40 of the toroidal transformer core is passed arigid conductor 36 surrounding and holding an insulated flexibleconductor 38, i.e. a wire, arranged here for carrying the line powercurrent through the circuit breaker and ending at a load terminal 18 (inphantom) for connection to a branch load line. This arrangement createsa so-called “faux coaxial conductor” for the ground fault currentsensing apparatus of the present invention. The rigid conductor 36 isconnected to a neutral return wire 26, sometimes known as a pig tail, ata first end 42 of the rigid conductor 36, as part of the neutral currentpath through the circuit breaker 30. The second end 44 of the rigidconnector 36 is formed into the Neutral terminal 28 of the circuitbreaker for connection to the neutral line of the branch load 22 (FIG.1).

The rigid connector 36 is mounted, e.g. soldered, to a printed circuitboard (PCB) 50 along with the various electronic components,collectively 52, necessary to perform the circuit interruption functionsof the breaker 30. Leads may be incorporated into the PCB 50 and makecontact with the rigid conductor 36 where it is soldered to the boardsuch as at one of its pins 57 (see FIG. 24), to be connected forproviding the current paths necessary to operate the breaker withoutexcessive use of jumper wires.

FIG. 5 illustrates a first alternative version 110 of the rigidconductor which fits into the tubular opening inside the center of thecurrent transformer and allows a second flexible conductor (38, FIG. 4)to pass through the center tubular portion 111 of the rigid conductor110.

FIGS. 6 and 7 illustrate a current flow 114 through the rigid conductor110. FIG. 7 shows the flat pattern of the conductor 110 before rollingof the center tubular portion 111 to create a tube. A pattern of holes,collectively 112, at each end of the tubular portion 111 redirects thecurrent flow through the center body area 113 to evenly distribute thecurrent flow lines 114 about the entire width, resulting in a controlledcurrent density and a substantially parallel direction of current flow.The well controlled current density and direction will produce a goodflux pattern 115 for minimal load shift error. This controlled area 113of the rigid conductor 110 will be located in the center of the GFIcurrent transformer 34 (FIG. 4) during operation.

The object of this design is to produce parallel paths of current flowto produce a well oriented flux pattern to offset the flux pattern ofthe flexible conductor wire inside the rigid conductor, with theresultant flux to be in line with the sensor core and windings. Thecurrent path of the captive flexible conductor (not shown) will produceflux lines in a direction that is in direct opposition to the rigidconductor current path.

FIG. 8 illustrates a basic construction second alternative 118 of rigidconductor wherein the unpierced broad central portion 119 of the flatconductor blank merely has its lateral edges folded into a tube withzero degrees of twist. However the current path in this basic embodimentwas found to be fairly uneven and was generally concentrated in astraight line between the ends.

FIG. 9 illustrates a third alternative version 120 of the rigidconductor with a rolled central portion 121 of zero degrees twistsimilar to that of FIG. 8 but with a slot 122 impressed in the tubularmiddle section 121 which redirects the current flow 123 to the outeredges of the tube. This design produced better flux patterns than thealternative of FIG. 8.

FIG. 10 illustrates a fourth alternative version 126 of the rigidconductor using three slots 127 instead of the one slot 122 in FIG. 9.These extra slots 127 provide a redirection of the current path 128 toachieve a different current distribution if desired.

FIG. 11 illustrates a fifth alternative version 130 of the rigidconductor. FIG. 12 is a flat pattern of the rigid conductor of FIG. 11showing the general current path 134 and flux pattern 135. The ends 131,132 of the rigid conductor 130 are 180 degrees out from one anothersince the middle section 133 has been put through a half roll twistduring formation from flat (FIG. 12) to tubular (FIG. 11). Thisembodiment was found to redirect the current flow for a good currentdensity distribution and flux pattern 135 throughout the centralportion.

FIGS. 13 and 14 illustrate a fifth alternative version 137 rigidconductor. The flat ends 138, 139 are not offset as the central tubularportion 140 was formed with a zero degree roll, i.e. without twisting.The wall areas of reduced cross sections 141 at each end of the rigidconductor tubular center 140 are an alternative to the holes of thealternatives shown in FIGS. 5, 9 and 10. These reduced cross sections141 will create resistance to current flow and will cause the current toseek a wider path as shown by the current lines 142 of FIG. 14.

FIGS. 15 and 16 illustrate a sixth alternative version 145 of the rigidconductor similar to the fifth alternative but with the reduced crosssections 146 shaped to create different resistance values in the center147 of the tubular body 148 versus the outer areas 149. The resistancevalue varies to cause the current flow to be evenly distributed aboutthe center portion 147 of the rigid conductor. Since current flowshighest in the least resistance path, the area of resistance of thecross section is varied to be higher in the center 147 and to offer theleast resistance on the outer areas 149 to achieve good distribution ofcurrent and flux path 150.

FIGS. 17 and 18 illustrate a seventh alternative 152 version of therigid conductor, The end tabs 153, 154 of the rigid conductor are 360degrees out from one another since the middle section 157 has been putthrough a full roll twist during formation from flat (FIG. 18) totubular (FIG. 17). This redirects the current flow 155 for a gooddensity distribution throughout the part. Arrows 156 show the generalflux direction which is noted to be at an angle to normal of the centralaxis of the conductor as a whole.

FIGS. 19 and 20 Illustrate an eighth alternative 158 of the rigidconductor. The end tabs, i.e. terminals 159, 160 of the rigid conductorare 270 degrees out from one another since the middle section 163 hasbeen put through a three-quarter roll twist during formation from flat(FIG. 20) to tubular (FIG. 19). Arrows 162 show the general fluxdirection which is noted to be at an angle to normal of the central axisof the conductor as a whole.

FIGS. 21 and 22 illustrate an ninth alternative 166 of the rigidconductor. The first end 167 of the center area 169 has a resistive area170 shaped by a reduced cross sectional area. The first end 167 forcesthe majority of the current 171 to be routed around the outer edges ofthe pocket 170 to the outer edges of the center section 169. Afterpassing the pocket 170 the current 171 is then free to travel diagonallyinward through the center section 169 to be brought together again atthe opposite end 168 of the center section 169 to achieve a changeddistribution of current 171 and flux 172 paths throughout the length ofthe rigid conductor 166. This construction will result in a differentflux output between the rigid conductor and captive flexible conductors,thus providing a different dispersion of flux to deliberately produce acurrent and consequent load shift output in the current transformersensor winding.

FIGS. 23, 24, and 25 show three possible variants 36 a, 36 b, 36 c ofthe rigid conductor 36 folded as if assembled into the faux co-axialconductors through the Ground Fault Interrupter current transformer. Aswill be understood from the foregoing discussion, each rigid conductor36 a, 36 b, 36 c can start as a flat plate-like part to be stamped,rolled and bent during the process of constructing the rigid conductorof the faux coax sensor package. In each variant, a first end 42 of therigid conductor 36 is rolled to form an open cylinder tubular connectionpoint 60 for a flexible wire within the breaker. While illustrated inthe foregoing description as carrying the Neutral current, it will beappreciated that the rigid conductor 36 could just as well carry theline current in other arrangements. A central tubular portion 62,unclosed here in all three variants, is formed by rolling a widercentral portion of the plate. The central tubular portion 62 of FIG. 23is rolled and/or twisted 180 degrees. The central tubular portion 62 ofFIG. 24 is rolled and/or twisted through 90 degrees and the centraltubular portion 62 of FIG. 25 has a so-called “zero degree” twist wherethe edges of the central plate are merely turned up towards one anotherwithout a twist through the axis of the starting plate. The centralportion 62 of FIG. 25 further has a feature 64 for adding resistance tocurrent flow stamped into the central portion as a reduced thickness ofthe wall section.

A multitude of variations for the faux coax concept could be utilized tooptimize load shift performance using variations of geometries; someexamples being coax shape, length, material thickness, etc.; to optimizevoltage drop at both typical 60Hz or 50Hz as well as at higher frequencysignatures during arcing faults.

The rigid conductor in conjunction with underlying PCB conductors mightfurther be used to replace separate jumper wire connections to themodule. For instance power and push-to-test (PTT) inputs could beincorporated through the rigid conductor rather than as jumper wires. Itwill also be appreciated that the body of the rigid conductor could beinsulated to reduce dielectric concerns to surrounding components. Againit will be appreciated that the rigid conductor 36 could be connectedthrough either the Line Power (hot) wire path or the Neutral Return wirepath in the construction of the faux coax arrangement.

While particular aspects, implementations, and applications of thepresent disclosure have been illustrated and described, it is to beunderstood that the present disclosure is not limited to the preciseconstruction and compositions disclosed herein and that variousmodifications, changes, and variations may be apparent from theforegoing descriptions without departing from the invention as definedin the appended claims.

1. A miniature circuit breaker of the arc fault sensing type comprising: a current transformer with an apertured magnetic core; electronics configured to detect ground faults; first and second primary conductors extending through the core; the first primary conductor being a substantially rigid conductor with a tubular portion located inside the core and further having nontubular second and third portions outside the core extending at angles to the tubular portion; the second primary conductor being a flexible wire held inside the tubular portion of the first primary conductor in a substantially coaxial arrangement; the current transformer further having a secondary winding comprising a plurality of turns on the core; and a trip circuit responsive to sensed signals on the secondary winding.
 2. The miniature circuit breaker of claim 1 wherein the tubular portion of the first primary conductor does not form a fully closed tube.
 3. The miniature circuit breaker of claim 1 wherein the electronics are mounted on a printed circuit board.
 4. The miniature circuit breaker of claim 1 wherein one of the second and third portions of the first primary conductor is attached to the printed circuit board.
 5. The miniature circuit breaker of claim 1 wherein the tubular portion of the first primary conductor comprises an electrical resistance feature configured to increase resistance to a flow of current through the first primary conductor.
 6. The miniature circuit breaker of claim 5 wherein the tubular portion of the first primary conductor comprises a plurality of electrical resistance features.
 7. The miniature circuit breaker of claim 5 wherein the electrical resistance feature is on only one end of the tubular portion.
 8. The miniature circuit breaker of claim 5 wherein the electrical resistance feature comprises a narrowed wall thickness in a section of the tubular portion.
 9. The miniature circuit breaker of claim 5 wherein the electrical resistance feature comprises a through hole in a section of the tubular portion.
 10. The miniature circuit breaker of claim 1 wherein the first primary conductor is connected to and forms a part of a neutral return power current path.
 11. The miniature circuit breaker of claim 1 wherein the first primary conductor is connected to line current.
 12. The miniature circuit breaker of claim 1 wherein the tubular portion of the first primary conductor is formed with a 0 degree twist.
 13. The miniature circuit breaker of claim 1 wherein the tubular portion of the first primary conductor is formed with a substantially 90 degree twist.
 14. The miniature circuit breaker of claim 1 wherein the tubular portion of the first primary conductor is formed with a substantially 180 degree twist.
 15. The miniature circuit break of claim 1 wherein one of the second and third portions of the first primary conductor is tubular. 